Ch 22: Speciation

Question 1

Define taxonomy, binomial nomenclature and explain why it is important

Answer 1

• Taxonomy: the branch of science concerned with classification, especially oforganisms
• Binomial nomenclature is a system used to name and identify organisms based on their genus and species names. This naming system is important becauseit allows scientists to keep an organized list of species and it allows them to track their numbers in an ecosystem.

Question 2

List the levels of the taxonomic hierarchy in order

Answer 2

Domain → Kingdom → Phylum → Class → Order → Family → Genus → species

Question 3

Define the biological species concept

Answer 3

A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring—but do not produce viable, fertile offspring with members of other such groups. Thus, the members of a biological species are united by being reproductively compatible, at least potentially.

Question 4

Explain why the biological species concept is widely used

Answer 4

This concept has no complexity.It explains why individuals from the same species group have the same structure or appearance; the biological species concept, with its focus on reproductive barriers, is particularly helpful.

Question 5

Describe the limitations of the biological species concept

Answer 5

• The biological species concept focuses on the separateness of different species due to reproductive barriers that lead to reproductive isolation.
  
  • The number of species to which this concept can be usefully applied is limited. The biological species concept also does not apply to organisms that reproduce asexually all or most of the time.

Question 6

Compare and contrast (similarities & differences between) biological, morphological, and ecological species concepts

Answer 6

• Biological Species Concept: A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring—but do not produce viable, fertile offspring with members of other such groups.
• Morphological Species Concept: A species is a set of organisms that look similar to each other and that are distinct from organisms in other sets.
• Ecological Species Concept: There is a one-to-one correspondence between a species and its niche.

Question 7

Explain the concept of reproductive isolation

Answer 7

• Reproductive isolation requires at least some sort of physical separation for long periods of time (10 – 100 000 years!) during which populations can diverge by developing different biological characters/ features that prevent them to interbreed.
  
  • These biological characteristics are called reproductive barriers
    
    • Speciation can happen WITH or WITHOUT physical separation – yet, in both cases gene flow stops

Question 8

List of Reproductive Barriers: Prezygotic (before fertilization)

Answer 8

• Pre-Mating:
  
  • Behavioral Isolation: populations of the same species begin to develop different behaviors that are not recognized or preferred by members in another population (mating calls)
  • Ecological Isolation: Populations may occupy the same territory but live in different habitats and so not meet.
  • Temporal Isolation: the differences in the timing of critical reproductive events prevent members of closely related species, which could otherwise breed with one another, from mating and producing hybrid offspring.
  • Mechanical Isolation: a physical incompatibility between reproductive organs of two organisms.
• Post-Mating
  - Gametic Isolation: gametes (egg and sperm) come into contact, but no fertilization takes place

Question 9

List of Reproductive Barriers: Postzygotic (After fertilization)

Answer 9

• (Occurs after fertilization)
  
  • Hybrid Inviability: reduces a hybrid’s capacity to mature into a healthy, fit adult.
  • Hybrid Sterility: Hybrid zygotes sometimes develop into adults but the adults fail to develop functional gametes and are sterile.
  • Hybrid Breakdown: First generation (F1) hybrids are viable and fertile, but further hybrid generations (F2 and backcrosses) may be inviable or sterile.

Question 10

Allopatric speciation

Answer 10

• In allopatric speciation, gene flow is interrupted when a population is divided into geographically isolated subpopulations.
• Can be caused by Founder effect (Genetic Drift)
  
  • Once physically separated, gene flow between the populations stops and divergence begins => new species
    
    • Can lead to: Adaptive radiation: Explosive (“rapid”) form of speciation leading to the formation of many new species due to “open” environmental conditions (when many new resources are “suddenly” available)
    • Can lead to: Co-Speciation: Occurs when two species that are very closely associated (ex: Host-parasite) speciate in response to each other and at the same time

Question 11

Sympatric Speciation

Answer 11

• In sympatric speciation, speciation occurs in populations that live in the same geographic area.
  
  • Sympatric speciation can occur if gene flow is reduced by such factors as polyploidy, habitat differentiation, and sexual selection.
    
    • Habitat differentiation: they occupy different components of the environment
    • Sexual selection: Ex: female preference for a certain vocal repertoire, or color, or behavior…
    • Polyploidy: due to error(s) during cell division that led to an extra set of chromosomes) – rare in animals but common in plants

Question 12

Compare and contrast allopatric and sympatric speciation

Answer 12

• In allopatric speciation, gene flow is interrupted when a population is divided into geographically isolated subpopulations.
• In sympatric speciation, speciation occurs in populations that live in the same geographic area.
  • Sympatric speciation can occur if gene flow is reduced by such factors as polyploidy, habitat differentiation, and sexual selection.

Question 13

Explain why speciation can be considered at the interface between micro- and macroevolution

Answer 13

• The time it takes for reproductive isolation to occur can vary
  
  • Speciation may occur almost instantaneously (in one generation) in plants as a result of polyploidy
  • Speciation in animals often takes much much longer- on the order of tens of thousands to millions of years
• Speciation forms a conceptual bridge between micro & macroevolution
  
  • Microevolution → Speciation → Macroevolution

Question 14

NOTES

Answer 14

• Allopatric speciation is more likely to occur when an isolated population small and exposed to different selection pressures in its new habitat.
• The biological species concept distinguishes two species by the degree of genetic exchange between their gene pools.
• Gene flow would not contribute to allopatric speciation.
• The last form of prezygotic barrier that could take place in maintaining reproductive isolation between two individuals is gametic isolation.
• Ecological/Habitat/Geological isolation is not a type of intrinsic reproductive isolation. (Mechanical, Behavioral, Gametic, Temporal are all intrinsic to organism)
• The founder effect is not a mechanism through which sympatric speciation could occur.
• When hybrids in a hybrid zone can breed with each other and with both parent species and also have equal fitness to the parent species, one would predict that the species will fuse.